Various graphical techniques have been used to provide a visual representation of complex circuit characteristics such as the transfer of reflection characteristics. One of these is the Bode diagram such as is shown in FIG. 1A. A polar representation is frequently more meaningful when dealing with characteristics such as the reflection characteristic since it can be more easily interpreted on a Smith chart, such as that shown in FIG. 1B. Polar diagrams can be generated over a small dynamic range by splitting the signal into its in-phase and quadrature-phase components, typically by synchronous detection, and coupling each component to the appropriate deflection plates of a CRT display. A typical circuit for this is shown in FIG. 2. This prior art method is fairly limited in that it is capable of handling only "single ended" signals over a fairly low dynamic range, e.g. 20dB, that is, the type of circuit cannot be used for ratio measurements.
In accordance with the preferred embodiment of the present invention, logarithmic convertors produce logarithmic output signals in response to two input signals. The difference between these two logarithmic signals is then obtained. This difference signal represents the log of the ratio of the two input signals. The difference signal is then input to an exponentiator. This expanded signal is then mixed with signals carrying phase information from the two input signals and is split into its orthogonal components to provide the control signals for the polar display. Thus, a polar display of the ratio of the magnitude and phase characteristics of two input signals is provided.